diff --git a/crypto/cmac/cmac.c b/crypto/cmac/cmac.c
index 88a323da9c7490ab82fa5c6a06c649627eb426fc..3e6afc70db085f86af24004efde95e32c6e11d8a 100644
--- a/crypto/cmac/cmac.c
+++ b/crypto/cmac/cmac.c
@@ -151,7 +151,7 @@ int CMAC_Init(CMAC_CTX *ctx, const void *key, size_t keylen,
 			return 0;
 		if (!M_EVP_EncryptInit_ex(&ctx->cctx, NULL, NULL, NULL, zero_iv))
 			return 0;
-		memset(ctx->tbl, 0, bl);
+		memset(ctx->tbl, 0, M_EVP_CIPHER_CTX_block_size(&ctx->cctx));
 		ctx->nlast_block = 0;
 		return 1;
 		}